List of things to memorize:
SaM - Thermistor Link to original
Thermistor are made of a thick layer of ceramic (semiconductor ) .They are very common, and cost less than RTDs .Structure Principle of operation we exploit the semi-conductive behavior of the ceramic material which gives us a thermally activated conductivity .Thermisotr have a negative TCR (Temperature Coefficient of Resisitance) or NTC (Negative Temperature Coefficient) TCR = d T d R ⋅ R 1 < 0 ***Formula of the thermistor’s resistance ***:R ( T ) = R A ⋅ e β ( T 1 − T A 1 )
Real World Measures
R A R ( T = T A )
T A ( T A = 300° K )
β ∈ [ 3000° K ÷ 5000° K ] Thermistor are of about 100 μ m
Temperature range : T ∈ [ − 50° C ÷ 150° C ] here instead is defined differently)Common values for the thermistor’s resistance: R ∈ [ 1.8 k \ohm ÷ 10 k \ohm ]
The conductivity of semiconductors also depends on temperature .Graph of the conductivity for n-type doped silicon Graph of the conductivity for metals Terminology
N D + NOTE : The ionazied term means the dopants that contribuite to conduction, so the “active” dopants.~Ex.: in case of donors the electron that from the “donors extrinsix band” (E D .
Equation T 1 = a + b ln ( R ) + c ln 3 ( R )
a = T A 1 − β l n ( R A ) b = β 1 c ≈ 0 β ∈ [ 3000° K ÷ 5000° K ]
Types of thermistor
Standard precision accuracy ∈ [ 0.1° C ÷ 0.2° C ] T RANGE ∈ [ 0° C ÷ 70° C ] Extra precision accuracy = 0.1° C T RANGE Ultra precision accuracy = 0.05° C T RANGE ∈ [ 0° C ÷ 50° C ]
